1. Field of the Invention
The present invention relates to blowout preventors commonly used in oil and gas drilling operations to seal fluids within the well bore. More particularly, the present invention relates to a sealing or packing element of a ram-type blowout preventer with improved metal inserts to prevent extrusion of the sealing element.
2. Description of the Background
Ram-type blowout preventers or BOPs are commonly provided on wellheads for sealing with pipe and thereby retaining high pressure within the well bore. The BOP commonly employs a pair of semi-circular ram rubbers, each of which move simultaneously for sealing engagement with the pipe in response to application of high fluid pressure to the opposing ram cylinders In the past decade, increased emphasis has been placed upon BOPs which are capable with sealing with variable diameter pipe, thereby minimizing the number of blowout preventors required at the drilling site.
Since at least the 1930's, those skilled in the art of blowout preventers have recognized the desirability of utilizing metal plates or segments which may be at least partially embedded within the ram rubber to increase the integrity of the seal under high pressure. These metal segments are typically arranged circumferentially about each semi-circular ram rubber, as disclosed in U.S. Pat. No. 2,035,925, and inherently move closer as the BOP rams move radially inward to engage the pipe. U.S. Pat. No. 3,434,729 discloses a BOP ram assembly, and teaches the use of metal plates spaced above and below the ram rubber to inhibit the extrusion of rubber under high pressure. Although the metal plates as disclosed in the '729 patent have been widely used, many BOP operators prefer the characteristics of BOP sealing elements which include a plurality of circumferentially-spaced metal inserts imbedded within the ram rubber.
BOP metal inserts are preferably provided adjacent both the upper and lower ends of each of the opposing BOP seals. A significant advantage of providing the elements at the lower end of the BOP seal is that the entire BOP sealing assembly may be inverted during an emergency, so that the bottom inserts are now the top inserts and serve to prevent extrusion of the sealing element and thereby retain the high pressure fluid within the well bore. Such metallic inserts functionally are provided in two general types: (1) inserts within the elastomeric sealing material which are adapted for engagement with the pipe which passes through the BOP, and (2) inserts which are not adapted to engage the BOP pipe but only reinforce the elastomeric or rubber seal, so that a layer of the rubber seal is provided between the radially inwardmost surface of the metal inserts and the pipe.
One type of metal inserts for a BOP seal is disclosed in U.S. Pat. No. 3,572,628. The inserts as shown in FIG. 8 of this patent are substantially I-shaped, with the upper and lower flanges of each insert positioned adjacent the upper and lower ends of the BOP sealing element. U.S. Pat. No. 2,609,836 discloses a blowout preventor with "control elements" that are either I-shaped, as shown in FIGS. 13-15, or are cup-shaped, as shown in FIGS. 39-42. One advantage of the cup-shaped control elements is that these elements may interlock. U.S. Pat. No. 3,915,424 discloses anti-extrusion elements which are positioned adjacent the upper and lower surfaces of the BOP seal, and overlap and interlock so that the radially inward-most surface of the elements contacts the pipe. A particular type of interlocking mechanism for anti-extrusion elements of a BOP seal is disclosed in U.S. Pat. No. 3,915,426.
Advantages are obtained by using metal inserts for a BOP seal wherein the upper metal inserts and the lower metal inserts are interconnected, in the manner of the I-beam design discussed above. Compared to separate upper and lower insert designs, less individual components of the seal assembly are used, and the I-beam design also promotes the uniform movement of the inserts toward the pipe. U.S. Pat. No. 3,958,808 discloses I-beam inserts as shown in FIG. 9 with "buttons" to better secure the metal inserts to the elastomeric material of the sealing element. U.S. Pat. No. 4,444,404 discloses a BOP packing element with I-beam metal inserts having "stair-stepped" flanges. U.S. Pat. No. 4,447,037 disclosed another version of I-beam inserts for a BOP seal, with the metal inserts having a configuration as shown in FIGS. 6 and 7 of this patent.
Prior art BOPs have disadvantages which have limited their acceptance in the oil and gas exploration industry. Some of the BOPs employ sealing assemblies which do not include circumferentially spaced metal inserts to minimize extrusion of the sealing material, while other BOPs employ metal plates above and below the rubber sealing element to control extrusion. Of the BOPs which utilize circumferentially spaced metal inserts, the type of inserts which fixedly interconnect an upper insert member to a lower insert member are generally preferred over those Which utilize separate upper and lower insert members. BOP sealing inserts which interlock, such that significant extrusions gaps are eliminated between adjacent members, and which uniformly close around the pipe to create a seal are preferred, although such BOP's are generally expensive. Improved techniques are thus required to provide a relatively low cost sealing assembly for a BOP which does not suffer from the disadvantages of the prior art, and which can effectively prevent extrusion of the BOP sealing material.
The disadvantages of the prior art are overcome by the present invention, and an improved blowout preventer, a sealing assembly for a blowout preventer, and metal inserts for the sealing assembly of a blowout preventer are hereinafter disclosed which overcome the disadvantages of prior art BOPs.